I recently rented a car over Labor Day holiday at Sky Harbor. The original quote for my economy size car with taxes and fees was $175.00 through www.carrental.com. I was ultimately charged $396.74.
Here are some the buyer beware elements you will need to look at before you fall into a similar hole. I was talked into an upgrade for the car "to deal better with the mountains" on the way to Flagstaff...this cost was $10/day. What they don't tell you is that the associated fees and taxes reflect an upgrade which turned out to be twice as much as what was quoted on www.car rental.com...
I also selected a collision damage "waiver" because I have my own insurance that covers rental cars. The word "waiver" usually connotes a release from payment. Not an extra $104 line item. A lot of this confusion could have been alleviated if the clerk had asked if a customer wanted "a waiver" and then added, "you will be charged $26/day for the waiver and nothing if you decline the waiver even if you have your own insurance."
When I had a discussion in person at the rental desk about these issues I was told "I signed" everything so I shouldn't be surprised. I think most people might recognize someone tired from a flight, someone who waited 45 minutes in line at the rental desk to get a car, someone who was told in addition to everything else that she would be charged $200 "as a deposit" and didn't aggregate everything in its small font and signed to keep the line moving. On the legal intelligence scale they are in the right. In the emotional and ethical intelligence scale there is room for discussion.
Buyer beware.